The general aim of the proposed research is to determine the effects of hallucinogenic (e.g., LSD), narcotic (e.g., morphine) and other (e.g., amphetamine, chlorpromazine) drugs on perceptual behavior. Specifically, an attempt will be made to 1) determine the extent to which drug-induced changes in perceptual behavior reflect alterations in sensitivity (sensory capacity) as opposed to alterations in judgment (response bias), 2) determine the extent to which drug-induced perceptual changes depend upon specific experimental parameters, including drug dose, sensory modality and stimulus intensity, and response-reinforcer contingencies, and 3) determine the neurochemical systems involved in mediating drug-induced perceptual changes. We plan to pursue these specific aims by developing and utilizing standardized perceptual tasks involving successive, two-choice, discretetrial discriminations. Rats and pigeons will serve as subjects, auditory, visual, and tactile (electric shock) stimuli will be used, and the effects of a range of doses of hallucinogenic, narcotic, and other drugs will be assessed under various conditions. Analysis of data within the framework of signal detection theory will be particularly valuable in pursuing specific aim 1, while aim 3 will necessitate conducting drug interaction studies.